Table 1 Interview questions and prompts according to the target behaviours and Michie’s COM-B model

Initiating breastfeeding/Initiating formula feeding

Capability

Can you remember how you felt about the idea of breastfeeding when you were pregnant? Did you know much about breastfeeding?

Opportunity

Did you receive any support or advice from anyone or anywhere about breastfeeding or formula feeding (Prompts: family, friends, media, antenatal education). If yes: What was the advice and support? Did it influence you?

Are most of your friends breastfeeding or formula feeding?

Motivation

When did you start thinking about whether you wanted to only breastfeed or formula feed him/her or do both? So you had/hadn’t planned on how you would feed your baby?

Prolonging breastfeeding/Introduce formula

Capability

Do you feel that you know how to breastfeed well now?

Do you feel confident about it? Why/why not?

Opportunity

Do you feel supported, practically or emotionally in (breast) feeding your baby?

What things have influenced you to continue breastfeeding (Prompts: nutritional content, convenience, sleep better with BF or formula, work, friends).

Motivation

Do you want to continue breastfeeding your baby?

Are you still planning on breastfeeding for X?

Best practice formula preparation and feeding practices/Suboptimal formula preparation and feeding practices

Capability

How do you know how to make up the formula?

Do you feel confident with formula feeding?

Opportunity

Are there any issues around formula feeding that you would like more advice on or feel unclear about?

Motivation

Which do you think is easier: Breast feeding or formula feeding?

Introducing solids later (at 6 months)/Introducing solids earlier (before 4 months)

Capability

How will you know when the timing is right?/How did you know when to introduce solid foods to your baby?

Opportunity

Were you provided with any support or advice from anyone or anywhere about when to introduce solids foods to your baby? Did any of the advice/support change the age at which you introduced solid foods?

What is normal within your social network- when do other mothers introduce solid foods? Has this influenced you?/Will this influence you?

Motivation

Do you want to introduce solids when your baby is a particular age?

What kinds of things influenced your plans? Probe: beliefs about the consequences of introducing solids at various ages.

It is recommended that babies should start solids food at around 6 months of age. How do you feel about this recommendation?

Introduce healthy first foods/Introduce unhealthy first foods

Capability

Do you feel that you know enough about what you should feed your baby?

How confident do you feel with feeding your baby now? Why/why not?

Opportunity

Have you been provided with any specific support or advice from anyone or anywhere about what foods to feed your baby? (Prompt: who? what advice? what would help?). Did it influence what you feed your baby?

Motivation

Is there anything in particular that you want your baby to eat?

How confident do you feel with feeding your baby now?

Feed to appetite/Use non-nutritive feeding

Capability

What kinds of things influenced your (settling) behaviours? Probe: Knowledge, perceived ability.

How do you know when to feed your baby? How do you know when your baby is hungry or full? How do you know how much to feed your baby?

Opportunity

Were you provided with any support or advice from anyone or anywhere about settling your baby?

Motivation

Do you find it [using milk or food to settle] effective?

Before having your baby had you thought about what techniques you might use to settle the baby? (Prompt: Did you think that milk/food might be something that you would use?)

Did you plan on stopping breastfeeding at a particular age? Do you want to stop breastfeeding your baby at that age?

Which do you think is easier: Breast feeding or formula feeding?

Is (stopping breastfeeding at a particular age) something you had planned on doing?